Add ability to import std module into expression parser to improve C++ debugging

[teemperor]

Summary

This patch is the MVP version of importing the std module into the expression parser to improve C++ debugging.

What happens in this patch is that we inject a @import std into our expression source code. We also
modify our internal Clang instance for parsing this expression to work with modules and debug info
at the same time (which is the main change in terms of LOC). We implicitly build the std module on the first use. The
C++ include paths for building are extracted from the debug info, which means that this currently only
works if the program is compiled with -glldb -fmodules and uses the std module. The C include paths
are currently specified by LLDB.

I enabled the tests currently only for libc++ and Linux because I could test this locally. I'll enable the tests
for other platforms once this has landed and doesn't break any bots (and I implemented the platform-specific
C include paths for them).

With this patch we can now:

• Build a libc++ as a module and import it into the expression parser.
• Read from the module while also referencing declarations from the debug info. E.g. std::abs(local_variable).

What doesn't work (yet):

• Merging debug info and C++ module declarations. E.g. std::vector<CustomClass> doesn't work.
• Pretty much anything that involves the ASTImporter and templated code. As the ASTImporter is used for saving the result declaration, this means that we can't

call yet any function that returns a non-trivial type.

• Use libstdc++ for this, as it requires multiple include paths and Clang only emits one include path per module. Also libstdc++ doesn't support Clang modules without patches.

[teemperor]

All the changes regarding extracting module include paths are probably superseded by Adrian's patch (which does the same thing nicer). So all the code related to GetModuleIncludes will be removed from this patch most likely.

[teemperor]

• Cleaned up setup method.

[shafik]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/main.cpp

2

Looks like you are relying on iostream to bring in cstdlib which is not guaranteed.

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

443

eLanguageTypeC_plus_plus_03?

[labath]

I don't know much about modules so these are just two comments I noticed from a quick glance:

• using both virtual and override on a method (like ExternalASTSourceWrapper does) is overkill. Drop virtual.
• Returning /usr/include from GetSystemIncludeDirectoriesForLanguage is going to be wrong for remote sessions. The platform instance should have a "sysroot" path stored somewhere (from platform select foo --sysroot=/bar), so it would be good to at least honor that. It might even be good to pass the sysroot as the --sysroot parameter to clang.

lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp

267

return directories by value?

[teemperor]

• Rebase on top of Adrian's patch (Thanks!)
• Addressed the feedback from Shafik/Pavel.

[teemperor]

@labath Thanks for the hint with the sysroot, but I'm not really sure what's the best way to test this. Making a whole fake sysroot that can be used to compile a std module seems overkill, and not sure if symlinking or so is a good approach either. I'm open to suggestions.

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/main.cpp

2

We actually always import the whole std module, not only the submodule that is used in the program. (Partly because we don't use the submodule visibility feature and partly because I don't see any disadvantage in doing that).

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/Makefile

4

Makefile.rules defines MANDATORY_MODULE_BUILD_FLAGS for this. Can you instead add -fimplicit-module-maps to that variable and use it here?

[teemperor]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/Makefile

4

Well, we would need to add -glldb (needed on Linux at least, where this is not default) and -fimplicit-module-maps to that flag (and maybe even -fcxx-modules on macOS, but I'm not sure about that). Also I'm not sure if we want to have -gmodules in the same flag set as the importing of std should also work without. What about a separate MANDATORY_CXXMODULE_BUILD_FLAGS that we use in all the tests?

[labath]

In D58125#1399474, @teemperor wrote:

@labath Thanks for the hint with the sysroot, but I'm not really sure what's the best way to test this. Making a whole fake sysroot that can be used to compile a std module seems overkill, and not sure if symlinking or so is a good approach either. I'm open to suggestions.

How much of the sysroot would you actually need to recreate? Would a modulemap file and a one or two simple headers be enough?

Since we're simply testing here that the prefix gets prepended, I am not too worried if we just don't test that. What would make this super-interesting for me is if it would enable testing of this feature without a hard dependency on having libc++ installed on their system (a lot of people on linux still don't have libc++ by default, or may have an older non-modularized version), so if the "sysroot" test could be made to run on those systems, it would be awesome. I am not sure though what would be needed to make that happen. I suspect this could be pretty tricky, since our test suite is not really prepared for that. The most tractable path may be via something like a core file. Like, open a core file, while specifying the sysroot, import @std, then try to display something, which would not be possible without it.

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/Makefile

4

That works for me. The bit I really care about is the -fmodules-cache-path. If we don't set it an incremental bot may blow up when upstream clang changes the serialization format.

[teemperor]

• Added sysroot test.
• Moved build flags into MANDATORY_CXXMODULE_BUILD_FLAGS make variable.

[teemperor]

• Remove libc++ dependency from sysroot test.
• Small format fix for sysroot Makefile

[aprantl]

lldb/include/lldb/Target/Platform.h

288

\param

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

293

$(MANDATORY_MODULE_BUILD_CFLAG) -cfxx-modules -glldb ?
Why is -fimplicit-module-maps only on the C++ case?

[teemperor]

• Refactored build flags.
• Fixed doxygen comment.

Yeah, the implicit module map flag wasn't actually necessary for the tests, thanks! For the Makefile, I had to create a utility variable as -gmodules shouldn't be necessary for our tests, so the new flags are not really a superset of the normal module flags.

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

36

what's that for?

[teemperor]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

36

I think that's how we set our executable as the target? It's frankly cargo-culted setup code that we use in a few hundred other tests.

[labath]

Thank you for writing the test. I think it's really great that we're able to test something like this without depending on the actual c++ library existing and supporting modules. (I think we should have more tests like that).

lldb/include/lldb/Expression/ExpressionSourceCode.h

25

ArrayRef<std::string> ?

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

257–262

I'm wondering why have you needed to do this (and whether we can figure out another solution to that).

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

254

Shouldn't this use the platform of the currently executed target (instead of the host platform)?

270–271

m_include_directories(std::move(include_directories))

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

480–490

all of this can boil down to something like:
LLDB_LOG(log, "Found module in compile unit: {0} - include dir: {1}", llvm::make_range(m.path.begin(), m.path.end()), m.search_path);

(i'd recommend using LLDB_LOG elsewhere too, but here the benefit is really obvious).

526–531

LLDB_LOG

[teemperor]

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

257–262

Yeah I should have added this as a comment to the test. Our sysroot system has only a few dummy headers, so we can resolve the #include <sys/prctl.h> in test_common.h. The removed -I flags are actually unintentional, I'll revert removing them.

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

36

lldbutil.run_break_set_by_file_and_line should be all you need. It has a.out as a default argument. So I don't think you need this line or the one defining exe, or the dictionary=... argument to build().

[labath]

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

257–262

Ah, cool. I suspected something like that. In that case I suggest also renaming the flag to NO_TEST_COMMON_H or something. (We should probably replace the force-include by an actual include some day.)

[teemperor]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

36

When I remove this line, I actually get AssertionError: False is not True : Expecting 1 locations, got 0 from the lldbutil.run_break_set_by_file_and_line.

I can't remember if I added the dictionary= argument for a specific reason or if that was just a side effect when debugging tests. Doesn't seem to break anything though, so I'll remove it.

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

36

Interesting. Looks like there are several very similarly named helper functions in lldbutil. There are several testcases that only use run_to_source/line_breakpoint without running file` manually, so perhaps those functions do more work than run_break_set_by_file_and_line. Since the line number comes from a regex anyway, I'd recommend using `run_to_source_breakpoint instead and also deleting the regex matching from setUp().

[teemperor]

• Addressed Pavel's comments (thanks!).
• Reworked test setup code (thanks Adrian!)
• Rebased the patch.

[labath]

Thanks Raphael. Apart from some inline nits, I have no further comments from my side, but hopefully someone with more familiarity with modules and clang ASTs can give this the final pass.

lldb/include/lldb/Expression/ExpressionSourceCode.h

13–16

It looks like these includes are no longer needed.

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp

279

const std::string & avoids a copy

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

480–481

I would actually say that make_range is better than join here, because it avoids constructing a temporary string. So, I'd just remove the FIXME here. (BTW, if you want to control the separator string, there's already a syntax for that: {0:$[.]})

[teemperor]

• Addressed Pavel's comments.

[aprantl]

This looks mostly good now.

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/TestImportStdModule.py

19

Do you understand why the "dwarf" is necessary?

lldb/source/Plugins/ExpressionParser/Clang/ASTUtils.h

428

std::for_each() or for (auto *S : Sources)?

[teemperor]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/TestImportStdModule.py

19

The test relies on having the module imports with their include directories listed in the debug info, which I think only dwarf supports for now? It fails for dwo at the moment and I guess there is no equivalent in PDB (can't test this though).

[aprantl]

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/TestImportStdModule.py

19

The debug info *format* should not have any semantic effect on the contents, so you probably found some kind of bug. At least dwarf and dwo should behave the same on Linux, as should dsym and dwarf on Darwin. PDB actually can have different contents because it's completely different; skippin gthat makes sense to me. Feel free to investigate this separately though.

[teemperor]

• Rebased patch.
• Modernized for loops in ASTUtils.

lldb/include/lldb/Expression/ExpressionSourceCode.h

 //===-- ExpressionSourceCode.h ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef liblldb_ExpressionSourceCode_h
 #define liblldb_ExpressionSourceCode_h
 
 #include "lldb/lldb-enumerations.h"
+#include "llvm/ADT/ArrayRef.h"
 
 #include <string>
 
 namespace lldb_private {
 
 class ExpressionSourceCode {
 public:
   bool NeedsWrapping() const { return m_wrap; }
 
   const char *GetName() const { return m_name.c_str(); }
 
 protected:
   ExpressionSourceCode(const char *name, const char *prefix, const char *body,
                        bool wrap)
       : m_name(name), m_prefix(prefix), m_body(body), m_wrap(wrap) {}
 
   std::string m_name;
   std::string m_prefix;
   std::string m_body;
   bool m_wrap;
 };
 
 } // namespace lldb_private
 
 #endif

lldb/include/lldb/Target/Platform.h

public:
   virtual ArchSpec GetRemoteSystemArchitecture() {
     return ArchSpec(); // Return an invalid architecture
   }
 
   virtual FileSpec GetRemoteWorkingDirectory() { return m_working_dir; }
 
   virtual bool SetRemoteWorkingDirectory(const FileSpec &working_dir);
 
+  //------------------------------------------------------------------
+  /// Retrieve the system include directories on this platform for the
+  /// given language.
+  ///
+  /// \param[in] lang
+  ///     The language for which the include directories should be queried.
+  ///
+  /// \param[out] directories
+  ///     The include directories for this system.
+  //------------------------------------------------------------------
+  virtual std::vector<std::string>
+  GetSystemIncludeDirectories(lldb::LanguageType lang) {
+    return {};
+  }
+
   virtual UserIDResolver &GetUserIDResolver() = 0;
 
   //------------------------------------------------------------------
   /// Locate a file for a platform.
   ///
   /// The default implementation of this function will return the same file
   /// patch in \a local_file as was in \a platform_file.
   ///

lldb/include/lldb/Target/Target.h

public:
   FileSpecList &GetExecutableSearchPaths();
 
   FileSpecList &GetDebugFileSearchPaths();
 
   FileSpecList &GetClangModuleSearchPaths();
 
   bool GetEnableAutoImportClangModules() const;
 
+  bool GetEnableImportStdModule() const;
+
   bool GetEnableAutoApplyFixIts() const;
 
   bool GetEnableNotifyAboutFixIts() const;
 
   bool GetEnableSaveObjects() const;
 
   bool GetEnableSyntheticValue() const;
 

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/Makefile

+LEVEL = ../../../make
+USE_LIBCPP := 1
+CXXFLAGS += $(MANDATORY_CXXMODULE_BUILD_CFLAGS)
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/TestImportStdModule.py

+"""
+Test importing the 'std' C++ module and evaluate expressions with it.
+"""
+
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class ImportStdModule(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    # FIXME: This should work on more setups, so remove these
+    # skipIf's in the future.
+    @add_test_categories(["libc++"])
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(oslist=no_match(["linux"]))
+    @skipIf(debug_info=no_match(["dwarf"]))
+    def test(self):
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(self,
+            "// Set break point at this line.", lldb.SBFileSpec("main.cpp"))
+
+        # Activate importing of std module.
+        self.runCmd("settings set target.import-std-module true")
+        # Calling some normal std functions that return non-template types.
+        self.expect("expr std::abs(-42)", substrs=['(int) $0 = 42'])
+        self.expect("expr std::div(2, 1).quot", substrs=['(int) $1 = 2'])
+        # Using types from std.
+        self.expect("expr (std::size_t)33U", substrs=['(size_t) $2 = 33'])
+        # Calling templated functions that return non-template types.
+        self.expect("expr char a = 'b'; char b = 'a'; std::swap(a, b); a",
+                    substrs=["(char) $3 = 'a'"])
+
+    # FIXME: This should work on more setups, so remove these
+    # skipIf's in the future.
+    @add_test_categories(["libc++"])
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(oslist=no_match(["linux"]))
+    @skipIf(debug_info=no_match(["dwarf"]))
+    def test_non_cpp_language(self):
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(self,
+            "// Set break point at this line.", lldb.SBFileSpec("main.cpp"))
+
+        # Activate importing of std module.
+        self.runCmd("settings set target.import-std-module true")
+        # These languages don't support C++ modules, so they shouldn't
+        # be able to evaluate the expression.
+        self.expect("expr -l C -- std::abs(-42)", error=True)
+        self.expect("expr -l C99 -- std::abs(-42)", error=True)
+        self.expect("expr -l C11 -- std::abs(-42)", error=True)
+        self.expect("expr -l ObjC -- std::abs(-42)", error=True)

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/basic/main.cpp

+// We need to import any std module. It doesn't matter which one.
+#include <iostream>
+
+int main(int argc, char **argv) {
+  std::cout << "Test" << std::endl;
+  return 0; // Set break point at this line.
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/Makefile

+LEVEL = ../../../make
+USE_LIBCPP := 1
+CXXFLAGS += $(MANDATORY_CXXMODULE_BUILD_CFLAGS)
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/TestStdModuleWithConflicts.py

+"""
+Test importing the 'std' C++ module and check if we can handle
+prioritizing the conflicting functions from debug info and std
+module.
+
+See also import-std-module/basic/TestImportStdModule.py for
+the same test on a 'clean' code base without conflicts.
+"""
+
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestImportStdModuleConflicts(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    # FIXME: This should work on more setups, so remove these
+    # skipIf's in the future.
+    @add_test_categories(["libc++"])
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(oslist=no_match(["linux"]))
+    @skipIf(debug_info=no_match(["dwarf"]))
+    def test(self):
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(self,
+            "// Set break point at this line.", lldb.SBFileSpec("main.cpp"))
+
+        self.runCmd("settings set target.import-std-module true")
+        self.expect("expr std::abs(-42)", substrs=['(int) $0 = 42'])
+        self.expect("expr std::div(2, 1).quot", substrs=['(int) $1 = 2'])
+        self.expect("expr (std::size_t)33U", substrs=['(size_t) $2 = 33'])
+        self.expect("expr char a = 'b'; char b = 'a'; std::swap(a, b); a",
+                    substrs=["(char) $3 = 'a'"])

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/conflicts/main.cpp

+#include <cstdlib>
+#include <utility>
+
+int main(int argc, char **argv) {
+  std::size_t f = argc;
+  f = std::abs(argc);
+  f = std::div(argc * 2, argc).quot;
+  std::swap(f, f);
+  return f; // Set break point at this line.
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/no-std-module/Makefile

+LEVEL = ../../../make
+USE_LIBCPP := 1
+CXXFLAGS += $(MANDATORY_CXXMODULE_BUILD_CFLAGS)
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/no-std-module/TestMissingStdModule.py

+"""
+Test that importing the std module on a compile unit
+that doesn't use the std module will not break LLDB.
+
+It's not really specified at the moment what kind of
+error we should report back to the user in this
+situation. Currently Clang will just complain that
+the std module doesn't exist or can't be loaded.
+"""
+
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class STLTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    # FIXME: This should work on more setups, so remove these
+    # skipIf's in the future.
+    @add_test_categories(["libc++"])
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(oslist=no_match(["linux"]))
+    @skipIf(debug_info=no_match(["dwarf"]))
+    def test(self):
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(self,
+            "// Set break point at this line.", lldb.SBFileSpec("main.cpp"))
+
+        # Activate importing of std module.
+        self.runCmd("settings set target.import-std-module true")
+
+        # Run some commands that should all fail without our std module.
+        self.expect("expr std::abs(-42)", error=True)
+        self.expect("expr std::div(2, 1).quot", error=True)
+        self.expect("expr (std::size_t)33U", error=True)
+        self.expect("expr char a = 'b'; char b = 'a'; std::swap(a, b); a",
+                    error=True)

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/no-std-module/main.cpp

+// We don't import any std module here.
+
+int main(int argc, char **argv) {
+  return 0; // Set break point at this line.
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/Makefile

+LEVEL = ../../../make
+# We don't have any standard include directories, so we can't
+# parse the test_common.h header we usually inject as it includes
+# system headers.
+NO_TEST_COMMON_H := 1
+
+CXXFLAGS += $(MANDATORY_CXXMODULE_BUILD_CFLAGS)
+CXXFLAGS += -I $(SRCDIR)/root/usr/include/c++/include/ -I $(SRCDIR)/root/usr/include/ -nostdinc -nostdinc++ -nostdlib++
+CXX_SOURCES := main.cpp
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/TestStdModuleSysroot.py

+"""
+Test that we respect the sysroot when building the std module.
+"""
+
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+import os
+
+class ImportStdModule(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    # FIXME: This should work on more setups, so remove these
+    # skipIf's in the future.
+    @skipIf(compiler=no_match("clang"))
+    @skipIf(oslist=no_match(["linux"]))
+    @skipIf(debug_info=no_match(["dwarf"]))
+    def test(self):
+        self.build()
+
+        sysroot = os.path.join(os.getcwd(), "root")
+
+        # Set the sysroot.
+        self.runCmd("platform select --sysroot '" + sysroot + "' host", CURRENT_EXECUTABLE_SET)
+
+        lldbutil.run_to_source_breakpoint(self,
+            "// Set break point at this line.", lldb.SBFileSpec("main.cpp"))
+
+        self.runCmd("settings set target.import-std-module true")
+
+        # Call our custom function in our sysroot std module.
+        # If this gives us the correct result, then we used the sysroot.
+        self.expect("expr std::myabs(-42)", substrs=['(int) $0 = 42'])

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/main.cpp

+#include <algorithm>
+
+int main(int argc, char **argv) {
+  libc_struct s;
+  return 0; // Set break point at this line.
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/root/usr/include/c++/include/algorithm

+#include "libc_header.h"
+
+namespace std {
+  int myabs(int i) {
+    return i < 0 ? -i : i;
+  }
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/root/usr/include/c++/include/module.modulemap

+module std {
+  module "algorithm" { header "algorithm" export * }
+}

lldb/packages/Python/lldbsuite/test/expression_command/import-std-module/sysroot/root/usr/include/libc_header.h

+struct libc_struct {};

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

 
 CFLAGS ?= $(DEBUG_INFO_FLAG) -O0 -fno-builtin
 ifeq "$(OS)" "Darwin"
   CFLAGS += $(ARCHFLAG) $(ARCH) $(FRAMEWORK_INCLUDES) -I$(LLDB_BASE_DIR)include
 else
   CFLAGS += $(ARCHFLAG)$(ARCH) $(FRAMEWORK_INCLUDES) -I$(LLDB_BASE_DIR)include
 endif
 
-CFLAGS += -I$(SRCDIR) -include $(THIS_FILE_DIR)test_common.h -I$(THIS_FILE_DIR)
+CFLAGS += -I$(SRCDIR) -I$(THIS_FILE_DIR)
+
+ifndef NO_TEST_COMMON_H
+  CFLAGS += -include $(THIS_FILE_DIR)test_common.h
+endif
+
 CFLAGS += $(NO_LIMIT_DEBUG_INFO_FLAGS) $(ARCH_CFLAGS) $(CFLAGS_EXTRAS)
 
 # If the OS is Windows, we need to pass -gdwarf to clang, otherwise it will build
 # with codeview by default but all the tests rely on dwarf.
 ifeq "$(OS)" "Windows_NT"
   CFLAGS += -gdwarf
 endif
 

 # Use a shared module cache when building in the default test build directory.
 CLANG_MODULE_CACHE_DIR := $(shell echo "$(BUILDDIR)" | sed $(QUOTE)s/lldb-test-build.noindex.*/lldb-test-build.noindex\/module-cache-clang/$(QUOTE))
 
 ifeq "$(findstring lldb-test-build.noindex, $(BUILDDIR))" ""
 CLANG_MODULE_CACHE_DIR := $(BUILDDIR)/module-cache
 $(warning failed to set the shared clang module cache dir)
 endif
 
-MANDATORY_MODULE_BUILD_CFLAGS := -fmodules -gmodules -fmodules-cache-path=$(CLANG_MODULE_CACHE_DIR)
+MODULE_BASE_FLAGS := -fmodules -gmodules -fmodules-cache-path=$(CLANG_MODULE_CACHE_DIR)
+MANDATORY_MODULE_BUILD_CFLAGS := $(MODULE_BASE_FLAGS) -gmodules
+# Build flags for building with C++ modules.
+# -glldb is necessary for emitting information about what modules were imported.
+MANDATORY_CXXMODULE_BUILD_CFLAGS := $(MODULE_BASE_FLAGS) -fcxx-modules -glldb
 
 ifeq "$(OS)" "Darwin"
   MANDATORY_MODULE_BUILD_CFLAGS += -fcxx-modules
 endif
 
 ifeq "$(MAKE_GMODULES)" "YES"
   CFLAGS += $(MANDATORY_MODULE_BUILD_CFLAGS)
   CXXFLAGS += $(MANDATORY_MODULE_BUILD_CFLAGS)

lldb/source/Plugins/ExpressionParser/Clang/ASTUtils.h

+//===-- ASTUtils.h ----------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef liblldb_ASTUtils_h_
+#define liblldb_ASTUtils_h_
+
+#include "clang/Sema/Lookup.h"
+#include "clang/Sema/MultiplexExternalSemaSource.h"
+#include "clang/Sema/Sema.h"
+#include "clang/Sema/SemaConsumer.h"
+
+namespace lldb_private {
+
+/// Wraps an ExternalASTSource into an ExternalSemaSource. Doesn't take
+/// ownership of the provided source.
+class ExternalASTSourceWrapper : public clang::ExternalSemaSource {
+  ExternalASTSource *m_Source;
+
+public:
+  ExternalASTSourceWrapper(ExternalASTSource *Source) : m_Source(Source) {
+    assert(m_Source && "Can't wrap nullptr ExternalASTSource");
+  }
+
+  ~ExternalASTSourceWrapper() override;
+
+  clang::Decl *GetExternalDecl(uint32_t ID) override {
+    return m_Source->GetExternalDecl(ID);
+  }
+
+  clang::Selector GetExternalSelector(uint32_t ID) override {
+    return m_Source->GetExternalSelector(ID);
+  }
+
+  uint32_t GetNumExternalSelectors() override {
+    return m_Source->GetNumExternalSelectors();
+  }
+
+  clang::Stmt *GetExternalDeclStmt(uint64_t Offset) override {
+    return m_Source->GetExternalDeclStmt(Offset);
+  }
+
+  clang::CXXCtorInitializer **
+  GetExternalCXXCtorInitializers(uint64_t Offset) override {
+    return m_Source->GetExternalCXXCtorInitializers(Offset);
+  }
+
+  clang::CXXBaseSpecifier *
+  GetExternalCXXBaseSpecifiers(uint64_t Offset) override {
+    return m_Source->GetExternalCXXBaseSpecifiers(Offset);
+  }
+
+  void updateOutOfDateIdentifier(clang::IdentifierInfo &II) override {
+    m_Source->updateOutOfDateIdentifier(II);
+  }
+
+  bool FindExternalVisibleDeclsByName(const clang::DeclContext *DC,
+                                      clang::DeclarationName Name) override {
+    return m_Source->FindExternalVisibleDeclsByName(DC, Name);
+  }
+
+  void completeVisibleDeclsMap(const clang::DeclContext *DC) override {
+    m_Source->completeVisibleDeclsMap(DC);
+  }
+
+  clang::Module *getModule(unsigned ID) override {
+    return m_Source->getModule(ID);
+  }
+
+  llvm::Optional<ASTSourceDescriptor>
+  getSourceDescriptor(unsigned ID) override {
+    return m_Source->getSourceDescriptor(ID);
+  }
+
+  ExtKind hasExternalDefinitions(const clang::Decl *D) override {
+    return m_Source->hasExternalDefinitions(D);
+  }
+
+  void FindExternalLexicalDecls(
+      const clang::DeclContext *DC,
+      llvm::function_ref<bool(clang::Decl::Kind)> IsKindWeWant,
+      llvm::SmallVectorImpl<clang::Decl *> &Result) override {
+    m_Source->FindExternalLexicalDecls(DC, IsKindWeWant, Result);
+  }
+
+  void
+  FindFileRegionDecls(clang::FileID File, unsigned Offset, unsigned Length,
+                      llvm::SmallVectorImpl<clang::Decl *> &Decls) override {
+    m_Source->FindFileRegionDecls(File, Offset, Length, Decls);
+  }
+
+  void CompleteRedeclChain(const clang::Decl *D) override {
+    m_Source->CompleteRedeclChain(D);
+  }
+
+  void CompleteType(clang::TagDecl *Tag) override {
+    m_Source->CompleteType(Tag);
+  }
+
+  void CompleteType(clang::ObjCInterfaceDecl *Class) override {
+    m_Source->CompleteType(Class);
+  }
+
+  void ReadComments() override { m_Source->ReadComments(); }
+
+  void StartedDeserializing() override { m_Source->StartedDeserializing(); }
+
+  void FinishedDeserializing() override { m_Source->FinishedDeserializing(); }
+
+  void StartTranslationUnit(clang::ASTConsumer *Consumer) override {
+    m_Source->StartTranslationUnit(Consumer);
+  }
+
+  void PrintStats() override;
+
+  bool layoutRecordType(
+      const clang::RecordDecl *Record, uint64_t &Size, uint64_t &Alignment,
+      llvm::DenseMap<const clang::FieldDecl *, uint64_t> &FieldOffsets,
+      llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
+          &BaseOffsets,
+      llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
+          &VirtualBaseOffsets) override {
+    return m_Source->layoutRecordType(Record, Size, Alignment, FieldOffsets,
+                                      BaseOffsets, VirtualBaseOffsets);
+  }
+};
+
+/// Wraps an ASTConsumer into an SemaConsumer. Doesn't take ownership of the
+/// provided consumer. If the provided ASTConsumer is also a SemaConsumer,
+/// the wrapper will also forward SemaConsumer functions.
+class ASTConsumerForwarder : public clang::SemaConsumer {
+  clang::ASTConsumer *m_c;
+  clang::SemaConsumer *m_sc;
+
+public:
+  ASTConsumerForwarder(clang::ASTConsumer *c) : m_c(c) {
+    m_sc = llvm::dyn_cast<clang::SemaConsumer>(m_c);
+  }
+
+  ~ASTConsumerForwarder() override;
+
+  void Initialize(clang::ASTContext &Context) override {
+    m_c->Initialize(Context);
+  }
+
+  bool HandleTopLevelDecl(clang::DeclGroupRef D) override {
+    return m_c->HandleTopLevelDecl(D);
+  }
+
+  void HandleInlineFunctionDefinition(clang::FunctionDecl *D) override {
+    m_c->HandleInlineFunctionDefinition(D);
+  }
+
+  void HandleInterestingDecl(clang::DeclGroupRef D) override {
+    m_c->HandleInterestingDecl(D);
+  }
+
+  void HandleTranslationUnit(clang::ASTContext &Ctx) override {
+    m_c->HandleTranslationUnit(Ctx);
+  }
+
+  void HandleTagDeclDefinition(clang::TagDecl *D) override {
+    m_c->HandleTagDeclDefinition(D);
+  }
+
+  void HandleTagDeclRequiredDefinition(const clang::TagDecl *D) override {
+    m_c->HandleTagDeclRequiredDefinition(D);
+  }
+
+  void HandleCXXImplicitFunctionInstantiation(clang::FunctionDecl *D) override {
+    m_c->HandleCXXImplicitFunctionInstantiation(D);
+  }
+
+  void HandleTopLevelDeclInObjCContainer(clang::DeclGroupRef D) override {
+    m_c->HandleTopLevelDeclInObjCContainer(D);
+  }
+
+  void HandleImplicitImportDecl(clang::ImportDecl *D) override {
+    m_c->HandleImplicitImportDecl(D);
+  }
+
+  void CompleteTentativeDefinition(clang::VarDecl *D) override {
+    m_c->CompleteTentativeDefinition(D);
+  }
+
+  void AssignInheritanceModel(clang::CXXRecordDecl *RD) override {
+    m_c->AssignInheritanceModel(RD);
+  }
+
+  void HandleCXXStaticMemberVarInstantiation(clang::VarDecl *D) override {
+    m_c->HandleCXXStaticMemberVarInstantiation(D);
+  }
+
+  void HandleVTable(clang::CXXRecordDecl *RD) override {
+    m_c->HandleVTable(RD);
+  }
+
+  clang::ASTMutationListener *GetASTMutationListener() override {
+    return m_c->GetASTMutationListener();
+  }
+
+  clang::ASTDeserializationListener *GetASTDeserializationListener() override {
+    return m_c->GetASTDeserializationListener();
+  }
+
+  void PrintStats() override;
+
+  void InitializeSema(clang::Sema &S) override {
+    if (m_sc)
+      m_sc->InitializeSema(S);
+  }
+
+  /// Inform the semantic consumer that Sema is no longer available.
+  void ForgetSema() override {
+    if (m_sc)
+      m_sc->ForgetSema();
+  }
+
+  bool shouldSkipFunctionBody(clang::Decl *D) override {
+    return m_c->shouldSkipFunctionBody(D);
+  }
+};
+
+/// A ExternalSemaSource multiplexer that prioritizes its sources.
+///
+/// This ExternalSemaSource will forward all requests to its attached sources.
+/// However, unlike a normal multiplexer it will not forward a request to all
+/// sources, but instead give priority to certain sources. If a source with a
+/// higher priority can fulfill a request, all sources with a lower priority
+/// will not receive the request.
+///
+/// This class is mostly use to multiplex between sources of different
+/// 'quality', e.g. a C++ modules and debug information. The C++ module will
+/// provide more accurate replies to the requests, but might not be able to
+/// answer all requests. The debug information will be used as a fallback then
+/// to provide information that is not in the C++ module.
+class SemaSourceWithPriorities : public clang::ExternalSemaSource {
+
+private:
+  /// The sources ordered in decreasing priority.
+  llvm::SmallVector<clang::ExternalSemaSource *, 2> Sources;
+
+public:
+  /// Construct a SemaSourceWithPriorities with a 'high quality' source that
+  /// has the higher priority and a 'low quality' source that will be used
+  /// as a fallback.
+  SemaSourceWithPriorities(clang::ExternalSemaSource &high_quality_source,
+                           clang::ExternalSemaSource &low_quality_source) {
+    Sources.push_back(&high_quality_source);
+    Sources.push_back(&low_quality_source);
+  }
+
+  ~SemaSourceWithPriorities() override;
+
+  void addSource(clang::ExternalSemaSource &source) {
+    Sources.push_back(&source);
+  }
+
+  //===--------------------------------------------------------------------===//
+  // ExternalASTSource.
+  //===--------------------------------------------------------------------===//
+
+  clang::Decl *GetExternalDecl(uint32_t ID) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (clang::Decl *Result = Sources[i]->GetExternalDecl(ID))
+        return Result;
+    return nullptr;
+  }
+
+  void CompleteRedeclChain(const clang::Decl *D) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->CompleteRedeclChain(D);
+  }
+
+  clang::Selector GetExternalSelector(uint32_t ID) override {
+    clang::Selector Sel;
+    for (size_t i = 0; i < Sources.size(); ++i) {
+      Sel = Sources[i]->GetExternalSelector(ID);
+      if (!Sel.isNull())
+        return Sel;
+    }
+    return Sel;
+  }
+
+  uint32_t GetNumExternalSelectors() override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (uint32_t total = Sources[i]->GetNumExternalSelectors())
+        return total;
+    return 0;
+  }
+
+  clang::Stmt *GetExternalDeclStmt(uint64_t Offset) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (clang::Stmt *Result = Sources[i]->GetExternalDeclStmt(Offset))
+        return Result;
+    return nullptr;
+  }
+
+  clang::CXXBaseSpecifier *
+  GetExternalCXXBaseSpecifiers(uint64_t Offset) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (clang::CXXBaseSpecifier *R =
+              Sources[i]->GetExternalCXXBaseSpecifiers(Offset))
+        return R;
+    return nullptr;
+  }
+
+  clang::CXXCtorInitializer **
+  GetExternalCXXCtorInitializers(uint64_t Offset) override {
+    for (auto *S : Sources)
+      if (auto *R = S->GetExternalCXXCtorInitializers(Offset))
+        return R;
+    return nullptr;
+  }
+
+  ExtKind hasExternalDefinitions(const clang::Decl *D) override {
+    for (const auto &S : Sources)
+      if (auto EK = S->hasExternalDefinitions(D))
+        if (EK != EK_ReplyHazy)
+          return EK;
+    return EK_ReplyHazy;
+  }
+
+  bool FindExternalVisibleDeclsByName(const clang::DeclContext *DC,
+                                      clang::DeclarationName Name) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (Sources[i]->FindExternalVisibleDeclsByName(DC, Name))
+        return true;
+    return false;
+  }
+
+  void completeVisibleDeclsMap(const clang::DeclContext *DC) override {
+    // FIXME: Only one source should be able to complete the decls map.
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->completeVisibleDeclsMap(DC);
+  }
+
+  void FindExternalLexicalDecls(
+      const clang::DeclContext *DC,
+      llvm::function_ref<bool(clang::Decl::Kind)> IsKindWeWant,
+      llvm::SmallVectorImpl<clang::Decl *> &Result) override {
+    for (size_t i = 0; i < Sources.size(); ++i) {
+      Sources[i]->FindExternalLexicalDecls(DC, IsKindWeWant, Result);
+      if (!Result.empty())
+        return;
+    }
+  }
+
+  void
+  FindFileRegionDecls(clang::FileID File, unsigned Offset, unsigned Length,
+                      llvm::SmallVectorImpl<clang::Decl *> &Decls) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->FindFileRegionDecls(File, Offset, Length, Decls);
+  }
+
+  void CompleteType(clang::TagDecl *Tag) override {
+    while (!Tag->isCompleteDefinition())
+      for (size_t i = 0; i < Sources.size(); ++i) {
+        // FIXME: We are technically supposed to loop here too until
+        // Tag->isCompleteDefinition() is true, but if our low quality source
+        // is failing to complete the tag this code will deadlock.
+        Sources[i]->CompleteType(Tag);
+        if (Tag->isCompleteDefinition())
+          break;
+      }
+  }
+
+  void CompleteType(clang::ObjCInterfaceDecl *Class) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->CompleteType(Class);
+  }
+
+  void ReadComments() override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadComments();
+  }
+
+  void StartedDeserializing() override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->StartedDeserializing();
+  }
+
+  void FinishedDeserializing() override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->FinishedDeserializing();
+  }
+
+  void StartTranslationUnit(clang::ASTConsumer *Consumer) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->StartTranslationUnit(Consumer);
+  }
+
+  void PrintStats() override;
+
+  clang::Module *getModule(unsigned ID) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (auto M = Sources[i]->getModule(ID))
+        return M;
+    return nullptr;
+  }
+
+  bool DeclIsFromPCHWithObjectFile(const clang::Decl *D) override {
+    for (auto *S : Sources)
+      if (S->DeclIsFromPCHWithObjectFile(D))
+        return true;
+    return false;
+  }
+
+  bool layoutRecordType(
+      const clang::RecordDecl *Record, uint64_t &Size, uint64_t &Alignment,
+      llvm::DenseMap<const clang::FieldDecl *, uint64_t> &FieldOffsets,
+      llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
+          &BaseOffsets,
+      llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
+          &VirtualBaseOffsets) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      if (Sources[i]->layoutRecordType(Record, Size, Alignment, FieldOffsets,
+                                       BaseOffsets, VirtualBaseOffsets))
+        return true;
+    return false;
+  }
+
+  void getMemoryBufferSizes(MemoryBufferSizes &sizes) const override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->getMemoryBufferSizes(sizes);
+  }
+
+  //===--------------------------------------------------------------------===//
+  // ExternalSemaSource.
+  //===--------------------------------------------------------------------===//
+
+  void InitializeSema(clang::Sema &S) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->InitializeSema(S);
+  }
+
+  void ForgetSema() override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ForgetSema();
+  }
+
+  void ReadMethodPool(clang::Selector Sel) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadMethodPool(Sel);
+  }
+
+  void updateOutOfDateSelector(clang::Selector Sel) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->updateOutOfDateSelector(Sel);
+  }
+
+  void ReadKnownNamespaces(
+      llvm::SmallVectorImpl<clang::NamespaceDecl *> &Namespaces) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadKnownNamespaces(Namespaces);
+  }
+
+  void ReadUndefinedButUsed(
+      llvm::MapVector<clang::NamedDecl *, clang::SourceLocation> &Undefined)
+      override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadUndefinedButUsed(Undefined);
+  }
+
+  void ReadMismatchingDeleteExpressions(
+      llvm::MapVector<clang::FieldDecl *,
+                      llvm::SmallVector<std::pair<clang::SourceLocation, bool>,
+                                        4>> &Exprs) override {
+    for (auto &Source : Sources)
+      Source->ReadMismatchingDeleteExpressions(Exprs);
+  }
+
+  bool LookupUnqualified(clang::LookupResult &R, clang::Scope *S) override {
+    for (size_t i = 0; i < Sources.size(); ++i) {
+      Sources[i]->LookupUnqualified(R, S);
+      if (!R.empty())
+        break;
+    }
+
+    return !R.empty();
+  }
+
+  void ReadTentativeDefinitions(
+      llvm::SmallVectorImpl<clang::VarDecl *> &Defs) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadTentativeDefinitions(Defs);
+  }
+
+  void ReadUnusedFileScopedDecls(
+      llvm::SmallVectorImpl<const clang::DeclaratorDecl *> &Decls) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadUnusedFileScopedDecls(Decls);
+  }
+
+  void ReadDelegatingConstructors(
+      llvm::SmallVectorImpl<clang::CXXConstructorDecl *> &Decls) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadDelegatingConstructors(Decls);
+  }
+
+  void ReadExtVectorDecls(
+      llvm::SmallVectorImpl<clang::TypedefNameDecl *> &Decls) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadExtVectorDecls(Decls);
+  }
+
+  void ReadUnusedLocalTypedefNameCandidates(
+      llvm::SmallSetVector<const clang::TypedefNameDecl *, 4> &Decls) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadUnusedLocalTypedefNameCandidates(Decls);
+  }
+
+  void ReadReferencedSelectors(
+      llvm::SmallVectorImpl<std::pair<clang::Selector, clang::SourceLocation>>
+          &Sels) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadReferencedSelectors(Sels);
+  }
+
+  void ReadWeakUndeclaredIdentifiers(
+      llvm::SmallVectorImpl<std::pair<clang::IdentifierInfo *, clang::WeakInfo>>
+          &WI) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadWeakUndeclaredIdentifiers(WI);
+  }
+
+  void ReadUsedVTables(
+      llvm::SmallVectorImpl<clang::ExternalVTableUse> &VTables) override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadUsedVTables(VTables);
+  }
+
+  void ReadPendingInstantiations(
+      llvm::SmallVectorImpl<
+          std::pair<clang::ValueDecl *, clang::SourceLocation>> &Pending)
+      override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadPendingInstantiations(Pending);
+  }
+
+  void ReadLateParsedTemplates(
+      llvm::MapVector<const clang::FunctionDecl *,
+                      std::unique_ptr<clang::LateParsedTemplate>> &LPTMap)
+      override {
+    for (size_t i = 0; i < Sources.size(); ++i)
+      Sources[i]->ReadLateParsedTemplates(LPTMap);
+  }
+
+  clang::TypoCorrection
+  CorrectTypo(const clang::DeclarationNameInfo &Typo, int LookupKind,
+              clang::Scope *S, clang::CXXScopeSpec *SS,
+              clang::CorrectionCandidateCallback &CCC,
+              clang::DeclContext *MemberContext, bool EnteringContext,
+              const clang::ObjCObjectPointerType *OPT) override {
+    for (size_t I = 0, E = Sources.size(); I < E; ++I) {
+      if (clang::TypoCorrection C =
+              Sources[I]->CorrectTypo(Typo, LookupKind, S, SS, CCC,
+                                      MemberContext, EnteringContext, OPT))
+        return C;
+    }
+    return clang::TypoCorrection();
+  }
+
+  bool MaybeDiagnoseMissingCompleteType(clang::SourceLocation Loc,
+                                        clang::QualType T) override {
+    for (size_t I = 0, E = Sources.size(); I < E; ++I) {
+      if (Sources[I]->MaybeDiagnoseMissingCompleteType(Loc, T))
+        return true;
+    }
+    return false;
+  }
+};
+
+} // namespace lldb_private
+#endif // liblldb_ASTUtils_h_

lldb/source/Plugins/ExpressionParser/Clang/ASTUtils.cpp

+//===-- ASTUtils.cpp --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "ASTUtils.h"
+
+lldb_private::ExternalASTSourceWrapper::~ExternalASTSourceWrapper() {}
+
+void lldb_private::ExternalASTSourceWrapper::PrintStats() {
+  m_Source->PrintStats();
+}
+
+lldb_private::ASTConsumerForwarder::~ASTConsumerForwarder() {}
+
+void lldb_private::ASTConsumerForwarder::PrintStats() { m_c->PrintStats(); }
+
+lldb_private::SemaSourceWithPriorities::~SemaSourceWithPriorities() {}
+
+void lldb_private::SemaSourceWithPriorities::PrintStats() {
+  for (size_t i = 0; i < Sources.size(); ++i)
+    Sources[i]->PrintStats();
+}

lldb/source/Plugins/ExpressionParser/Clang/CMakeLists.txt

 if(NOT LLDB_BUILT_STANDALONE)
   set(tablegen_deps intrinsics_gen)
 endif()
 
 add_lldb_library(lldbPluginExpressionParserClang PLUGIN
   ASTDumper.cpp
   ASTResultSynthesizer.cpp
   ASTStructExtractor.cpp
+  ASTUtils.cpp
   ClangASTSource.cpp
   ClangExpressionDeclMap.cpp
   ClangExpressionParser.cpp
   ClangExpressionSourceCode.cpp
   ClangExpressionVariable.cpp
   ClangFunctionCaller.cpp
   ClangHost.cpp
   ClangModulesDeclVendor.cpp

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.h

public:
   ///
   /// @param[in] exe_scope,
   ///     If non-NULL, an execution context scope that can help to
   ///     correctly create an expression with a valid process for
   ///     optional tuning Objective-C runtime support. Can be NULL.
   ///
   /// @param[in] expr
   ///     The expression to be parsed.
+  ///
+  /// @param[in] include_directories
+  ///     List of include directories that should be used when parsing the
+  ///     expression.
   //------------------------------------------------------------------
   ClangExpressionParser(ExecutionContextScope *exe_scope, Expression &expr,
-                        bool generate_debug_info);
+                        bool generate_debug_info,
+                        std::vector<ConstString> include_directories = {});
 
   //------------------------------------------------------------------
   /// Destructor
   //------------------------------------------------------------------
   ~ClangExpressionParser() override;
 
   bool Complete(CompletionRequest &request, unsigned line, unsigned pos,
                 unsigned typed_pos) override;
std::unique_ptr<clang::CompilerInstance>
       m_compiler; ///< The Clang compiler used to parse expressions into IR
   std::unique_ptr<clang::CodeGenerator>
       m_code_generator; ///< The Clang object that generates IR
 
   class LLDBPreprocessorCallbacks;
   LLDBPreprocessorCallbacks *m_pp_callbacks; ///< Called when the preprocessor
                                              ///encounters module imports
   std::unique_ptr<ClangASTContext> m_ast_context;
+
+  std::vector<ConstString> m_include_directories;
 };
 }
 
 #endif // liblldb_ClangExpressionParser_h_

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

 #include "clang/Rewrite/Core/Rewriter.h"
 #include "clang/Rewrite/Frontend/FrontendActions.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaConsumer.h"
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/TargetSelect.h"
 
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wglobal-constructors"
 #include "llvm/ExecutionEngine/MCJIT.h"
 #pragma clang diagnostic pop
 
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/DynamicLibrary.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Signals.h"
 
+#include "ClangDiagnostic.h"
+#include "ClangExpressionParser.h"
+#include "ClangUserExpression.h"
+
+#include "ASTUtils.h"
 #include "ClangASTSource.h"
 #include "ClangDiagnostic.h"
 #include "ClangExpressionDeclMap.h"
 #include "ClangExpressionHelper.h"
 #include "ClangExpressionParser.h"
+#include "ClangHost.h"
 #include "ClangModulesDeclVendor.h"
 #include "ClangPersistentVariables.h"
 #include "IRForTarget.h"
 #include "ModuleDependencyCollector.h"
 
 #include "lldb/Core/Debugger.h"
 #include "lldb/Core/Disassembler.h"
 #include "lldb/Core/Module.h"
public:
 
   clang::TextDiagnosticBuffer *GetPassthrough() { return m_passthrough.get(); }
 
 private:
   DiagnosticManager *m_manager = nullptr;
   std::shared_ptr<clang::TextDiagnosticBuffer> m_passthrough;
 };
 
+static void
+SetupModuleHeaderPaths(CompilerInstance *compiler,
+                       std::vector<ConstString> include_directories,
+                       lldb::TargetSP target_sp) {
+  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+
+  HeaderSearchOptions &search_opts = compiler->getHeaderSearchOpts();
+
+  for (ConstString dir : include_directories) {
+    search_opts.AddPath(dir.AsCString(), frontend::System, false, true);
+    LLDB_LOG(log, "Added user include dir: {0}", dir);
+  }
+
+  llvm::SmallString<128> module_cache;
+  auto props = ModuleList::GetGlobalModuleListProperties();
+  props.GetClangModulesCachePath().GetPath(module_cache);
+  search_opts.ModuleCachePath = module_cache.str();
+  LLDB_LOG(log, "Using module cache path: {0}", module_cache.c_str());
+
+  FileSpec clang_resource_dir = GetClangResourceDir();
+  std::string resource_dir = clang_resource_dir.GetPath();
+  if (FileSystem::Instance().IsDirectory(resource_dir)) {
+    search_opts.ResourceDir = resource_dir;
+    std::string resource_include = resource_dir + "/include";
+    search_opts.AddPath(resource_include, frontend::System, false, true);
+
+    LLDB_LOG(log, "Added resource include dir: {0}", resource_include);
+  }
+
+  search_opts.ImplicitModuleMaps = true;
+
+  std::vector<std::string> system_include_directories =
+      target_sp->GetPlatform()->GetSystemIncludeDirectories(
+          lldb::eLanguageTypeC_plus_plus);
+
+  for (const std::string &include_dir : system_include_directories) {
+    search_opts.AddPath(include_dir, frontend::System, false, true);
+
+    LLDB_LOG(log, "Added system include dir: {0}", include_dir);
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // Implementation of ClangExpressionParser
 //===----------------------------------------------------------------------===//
 
-ClangExpressionParser::ClangExpressionParser(ExecutionContextScope *exe_scope,
-                                             Expression &expr,
-                                             bool generate_debug_info)
+ClangExpressionParser::ClangExpressionParser(
+    ExecutionContextScope *exe_scope, Expression &expr,
+    bool generate_debug_info, std::vector<ConstString> include_directories)
     : ExpressionParser(exe_scope, expr, generate_debug_info), m_compiler(),
-      m_pp_callbacks(nullptr) {
+      m_pp_callbacks(nullptr),
+      m_include_directories(std::move(include_directories)) {
   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
 
   // We can't compile expressions without a target.  So if the exe_scope is
   // null or doesn't have a target, then we just need to get out of here.  I'll
   // lldb_assert and not make any of the compiler objects since
   // I can't return errors directly from the constructor.  Further calls will
   // check if the compiler was made and
   // bag out if it wasn't.
ClangExpressionParser::ClangExpressionParser(
   lang_opts.CharIsSigned = ArchSpec(m_compiler->getTargetOpts().Triple.c_str())
                                .CharIsSignedByDefault();
 
   // Spell checking is a nice feature, but it ends up completing a lot of types
   // that we didn't strictly speaking need to complete. As a result, we spend a
   // long time parsing and importing debug information.
   lang_opts.SpellChecking = false;
 
+  auto &clang_expr = *static_cast<ClangUserExpression *>(&m_expr);
+  if (clang_expr.DidImportCxxModules()) {
+    LLDB_LOG(log, "Adding lang options for importing C++ modules");
+
+    lang_opts.Modules = true;
+    // We want to implicitly build modules.
+    lang_opts.ImplicitModules = true;
+    // To automatically import all submodules when we import 'std'.
+    lang_opts.ModulesLocalVisibility = false;
+
+    // We use the @import statements, so we need this:
+    // FIXME: We could use the modules-ts, but that currently doesn't work.
+    lang_opts.ObjC = true;
+
+    // Options we need to parse libc++ code successfully.
+    // FIXME: We should ask the driver for the appropriate default flags.
+    lang_opts.GNUMode = true;
+    lang_opts.GNUKeywords = true;
+    lang_opts.DoubleSquareBracketAttributes = true;
+    lang_opts.CPlusPlus11 = true;
+
+    SetupModuleHeaderPaths(m_compiler.get(), m_include_directories,
+                           target_sp);
+  }
+
   if (process_sp && lang_opts.ObjC) {
     if (process_sp->GetObjCLanguageRuntime()) {
       if (process_sp->GetObjCLanguageRuntime()->GetRuntimeVersion() ==
           ObjCLanguageRuntime::ObjCRuntimeVersions::eAppleObjC_V2)
         lang_opts.ObjCRuntime.set(ObjCRuntime::MacOSX, VersionTuple(10, 7));
       else
         lang_opts.ObjCRuntime.set(ObjCRuntime::FragileMacOSX,
                                   VersionTuple(10, 7));
ClangExpressionParser::ClangExpressionParser(
   auto &PP = m_compiler->getPreprocessor();
   auto &builtin_context = PP.getBuiltinInfo();
   builtin_context.initializeBuiltins(PP.getIdentifierTable(),
                                      m_compiler->getLangOpts());
 
   m_compiler->createASTContext();
   clang::ASTContext &ast_context = m_compiler->getASTContext();
 
-  ClangExpressionHelper *type_system_helper =
-      dyn_cast<ClangExpressionHelper>(m_expr.GetTypeSystemHelper());
-  ClangExpressionDeclMap *decl_map = type_system_helper->DeclMap();
-
-  if (decl_map) {
-    llvm::IntrusiveRefCntPtr<clang::ExternalASTSource> ast_source(
-        decl_map->CreateProxy());
-    decl_map->InstallASTContext(ast_context, m_compiler->getFileManager());
-    ast_context.setExternalSource(ast_source);
-  }
-
   m_ast_context.reset(
       new ClangASTContext(m_compiler->getTargetOpts().Triple.c_str()));
   m_ast_context->setASTContext(&ast_context);
 
   std::string module_name("$__lldb_module");
 
   m_llvm_context.reset(new LLVMContext());
   m_code_generator.reset(CreateLLVMCodeGen(
ClangExpressionParser::ParseInternal(DiagnosticManager &diagnostic_manager,
   }
 
   diag_buf->BeginSourceFile(m_compiler->getLangOpts(),
                             &m_compiler->getPreprocessor());
 
   ClangExpressionHelper *type_system_helper =
       dyn_cast<ClangExpressionHelper>(m_expr.GetTypeSystemHelper());
 
-  ASTConsumer *ast_transformer =
-      type_system_helper->ASTTransformer(m_code_generator.get());
-
-  if (ClangExpressionDeclMap *decl_map = type_system_helper->DeclMap())
-    decl_map->InstallCodeGenerator(m_code_generator.get());
-
   // If we want to parse for code completion, we need to attach our code
   // completion consumer to the Sema and specify a completion position.
   // While parsing the Sema will call this consumer with the provided
   // completion suggestions.
   if (completion_consumer) {
     auto main_file = source_mgr.getFileEntryForID(source_mgr.getMainFileID());
     auto &PP = m_compiler->getPreprocessor();
     // Lines and columns start at 1 in Clang, but code completion positions are
     // indexed from 0, so we need to add 1 to the line and column here.
     ++completion_line;
     ++completion_column;
     PP.SetCodeCompletionPoint(main_file, completion_line, completion_column);
   }
 
+  ASTConsumer *ast_transformer =
+      type_system_helper->ASTTransformer(m_code_generator.get());
+
+  std::unique_ptr<clang::ASTConsumer> Consumer;
   if (ast_transformer) {
-    ast_transformer->Initialize(m_compiler->getASTContext());
-    ParseAST(m_compiler->getPreprocessor(), ast_transformer,
-             m_compiler->getASTContext(), false, TU_Complete,
-             completion_consumer);
+    Consumer.reset(new ASTConsumerForwarder(ast_transformer));
+  } else if (m_code_generator) {
+    Consumer.reset(new ASTConsumerForwarder(m_code_generator.get()));
+  } else {
+    Consumer.reset(new ASTConsumer());
+  }
+
+  clang::ASTContext &ast_context = m_compiler->getASTContext();
+
+  m_compiler->setSema(new Sema(m_compiler->getPreprocessor(), ast_context,
+                               *Consumer, TU_Complete, completion_consumer));
+  m_compiler->setASTConsumer(std::move(Consumer));
+
+  if (ast_context.getLangOpts().Modules)
+    m_compiler->createModuleManager();
+
+  ClangExpressionDeclMap *decl_map = type_system_helper->DeclMap();
+  if (decl_map) {
+    decl_map->InstallCodeGenerator(&m_compiler->getASTConsumer());
+
+    clang::ExternalASTSource *ast_source = decl_map->CreateProxy();
+
+    if (ast_context.getExternalSource()) {
+      auto module_wrapper =
+          new ExternalASTSourceWrapper(ast_context.getExternalSource());
+
+      auto ast_source_wrapper = new ExternalASTSourceWrapper(ast_source);
+
+      auto multiplexer =
+          new SemaSourceWithPriorities(*module_wrapper, *ast_source_wrapper);
+      IntrusiveRefCntPtr<ExternalASTSource> Source(multiplexer);
+      ast_context.setExternalSource(Source);
     } else {
-    m_code_generator->Initialize(m_compiler->getASTContext());
-    ParseAST(m_compiler->getPreprocessor(), m_code_generator.get(),
-             m_compiler->getASTContext(), false, TU_Complete,
-             completion_consumer);
+      ast_context.setExternalSource(ast_source);
+    }
+    decl_map->InstallASTContext(ast_context, m_compiler->getFileManager());
   }
 
+  // Check that the ASTReader is properly attached to ASTContext and Sema.
+  if (ast_context.getLangOpts().Modules) {
+    assert(m_compiler->getASTContext().getExternalSource() &&
+           "ASTContext doesn't know about the ASTReader?");
+    assert(m_compiler->getSema().getExternalSource() &&
+           "Sema doesn't know about the ASTReader?");
+  }
+
+  {
+    llvm::CrashRecoveryContextCleanupRegistrar<Sema> CleanupSema(
+        &m_compiler->getSema());
+    ParseAST(m_compiler->getSema(), false, false);
+  }
+  // Destroy the Sema. This is necessary because we want to emulate the
+  // original behavior of ParseAST (which also destroys the Sema after parsing).
+  m_compiler->setSema(nullptr);
+
   diag_buf->EndSourceFile();
 
   unsigned num_errors = diag_buf->getNumErrors();
 
   if (m_pp_callbacks && m_pp_callbacks->hasErrors()) {
     num_errors++;
     diagnostic_manager.PutString(eDiagnosticSeverityError,
                                  "while importing modules:");

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.h

public:
 
   static ClangExpressionSourceCode *CreateWrapped(const char *prefix,
                                              const char *body) {
     return new ClangExpressionSourceCode("$__lldb_expr", prefix, body, true);
   }
 
   uint32_t GetNumBodyLines();
 
+  /// Generates the source code that will evaluate the expression.
+  ///
+  /// \param text output parameter containing the source code string.
+  /// \param wrapping_language If the expression is supossed to be wrapped,
+  ///        then this is the language that should be used for that.
+  /// \param static_method True iff the expression is valuated inside a static
+  ///        Objective-C method.
+  /// \param exe_ctx The execution context in which the expression will be
+  ///        evaluated.
+  /// \param add_locals True iff local variables should be injected into the
+  ///        expression source code.
+  /// \param modules A list of (C++) modules that the expression should import.
+  ///
+  /// \return true iff the source code was successfully generated.
   bool GetText(std::string &text, lldb::LanguageType wrapping_language,
                bool static_method,
                ExecutionContext &exe_ctx,
-               bool add_locals) const;
+               bool add_locals,
+               llvm::ArrayRef<std::string> modules) const;
 
   // Given a string returned by GetText, find the beginning and end of the body
   // passed to CreateWrapped. Return true if the bounds could be found.  This
   // will also work on text with FixItHints applied.
   static bool GetOriginalBodyBounds(std::string transformed_text,
                                     lldb::LanguageType wrapping_language,
                                     size_t &start_loc, size_t &end_loc);
 

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionSourceCode.cpp

for (size_t i = 0; i < var_list_sp->GetSize(); i++) {
 
     stream.Printf("using $__lldb_local_vars::%s;\n", var_name.AsCString());
   }
 }
 
 bool ClangExpressionSourceCode::GetText(std::string &text,
                                    lldb::LanguageType wrapping_language,
                                    bool static_method,
-                                   ExecutionContext &exe_ctx,
-                                   bool add_locals) const {
+                                   ExecutionContext &exe_ctx, bool add_locals,
+                                   llvm::ArrayRef<std::string> modules) const {
   const char *target_specific_defines = "typedef signed char BOOL;\n";
   std::string module_macros;
 
   Target *target = exe_ctx.GetTargetPtr();
   if (target) {
     if (target->GetArchitecture().GetMachine() == llvm::Triple::aarch64) {
       target_specific_defines = "typedef bool BOOL;\n";
     }
if (m_wrap) {
     default:
       return false;
     case lldb::eLanguageTypeC:
     case lldb::eLanguageTypeC_plus_plus:
     case lldb::eLanguageTypeObjC:
       break;
     }
 
+    // Generate a list of @import statements that will import the specified
+    // module into our expression.
+    std::string module_imports;
+    for (const std::string &module : modules) {
+      module_imports.append("@import ");
+      module_imports.append(module);
+      module_imports.append(";\n");
+    }
+
     StreamString wrap_stream;
 
     wrap_stream.Printf("%s\n%s\n%s\n%s\n%s\n", module_macros.c_str(),
                        debug_macros_stream.GetData(), g_expression_prefix,
                        target_specific_defines, m_prefix.c_str());
 
     // First construct a tagged form of the user expression so we can find it
     // later:
case lldb::eLanguageTypeObjC:
       tagged_body.append(m_body);
       tagged_body.append(c_end_marker);
       break;
     }
     switch (wrapping_language) {
     default:
       break;
     case lldb::eLanguageTypeC:
-      wrap_stream.Printf("void                           \n"
+      wrap_stream.Printf("%s"
+                         "void                           \n"
                          "%s(void *$__lldb_arg)          \n"
                          "{                              \n"
                          "    %s;                        \n"
                          "%s"
                          "}                              \n",
-                         m_name.c_str(), lldb_local_var_decls.GetData(),
-                         tagged_body.c_str());
+                         module_imports.c_str(), m_name.c_str(),
+                         lldb_local_var_decls.GetData(), tagged_body.c_str());
       break;
     case lldb::eLanguageTypeC_plus_plus:
-      wrap_stream.Printf("void                                   \n"
+      wrap_stream.Printf("%s"
+                         "void                                   \n"
                          "$__lldb_class::%s(void *$__lldb_arg)   \n"
                          "{                                      \n"
                          "    %s;                                \n"
                          "%s"
                          "}                                      \n",
-                         m_name.c_str(), lldb_local_var_decls.GetData(),
-                         tagged_body.c_str());
+                         module_imports.c_str(), m_name.c_str(),
+                         lldb_local_var_decls.GetData(), tagged_body.c_str());
       break;
     case lldb::eLanguageTypeObjC:
       if (static_method) {
         wrap_stream.Printf(
+            "%s"
             "@interface $__lldb_objc_class ($__lldb_category)        \n"
             "+(void)%s:(void *)$__lldb_arg;                          \n"
             "@end                                                    \n"
             "@implementation $__lldb_objc_class ($__lldb_category)   \n"
             "+(void)%s:(void *)$__lldb_arg                           \n"
             "{                                                       \n"
             "%s"
             "}                                                       \n"
             "@end                                                    \n",
-            m_name.c_str(), m_name.c_str(), tagged_body.c_str());
+            module_imports.c_str(), m_name.c_str(), m_name.c_str(),
+            tagged_body.c_str());
       } else {
         wrap_stream.Printf(
+            "%s"
             "@interface $__lldb_objc_class ($__lldb_category)       \n"
             "-(void)%s:(void *)$__lldb_arg;                         \n"
             "@end                                                   \n"
             "@implementation $__lldb_objc_class ($__lldb_category)  \n"
             "-(void)%s:(void *)$__lldb_arg                          \n"
             "{                                                      \n"
             "%s"
             "}                                                      \n"
             "@end                                                   \n",
-            m_name.c_str(), m_name.c_str(), tagged_body.c_str());
+            module_imports.c_str(), m_name.c_str(), m_name.c_str(),
+            tagged_body.c_str());
       }
       break;
     }
 
     text = wrap_stream.GetString();
   } else {
     text.append(m_body);
   }

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.h

void ResetDeclMap(ExecutionContext &exe_ctx,
     m_type_system_helper.ResetDeclMap(exe_ctx, result_delegate,
                                       keep_result_in_memory,
                                       m_ctx_obj);
   }
 
   lldb::ExpressionVariableSP
   GetResultAfterDematerialization(ExecutionContextScope *exe_scope) override;
 
+  bool DidImportCxxModules() const { return m_imported_cpp_modules; }
+
 private:
   //------------------------------------------------------------------
   /// Populate m_in_cplusplus_method and m_in_objectivec_method based on the
   /// environment.
   //------------------------------------------------------------------
 
   void ScanContext(ExecutionContext &exe_ctx,
                    lldb_private::Status &err) override;
 
   bool AddArguments(ExecutionContext &exe_ctx, std::vector<lldb::addr_t> &args,
                     lldb::addr_t struct_address,
                     DiagnosticManager &diagnostic_manager) override;
 
+  std::vector<std::string> GetModulesToImport(ExecutionContext &exe_ctx);
   void UpdateLanguageForExpr(DiagnosticManager &diagnostic_manager,
-                             ExecutionContext &exe_ctx);
+                             ExecutionContext &exe_ctx,
+                             std::vector<std::string> modules_to_import);
   bool SetupPersistentState(DiagnosticManager &diagnostic_manager,
                                    ExecutionContext &exe_ctx);
   bool PrepareForParsing(DiagnosticManager &diagnostic_manager,
                          ExecutionContext &exe_ctx);
 
   ClangUserExpressionHelper m_type_system_helper;
 
   class ResultDelegate : public Materializer::PersistentVariableDelegate {
   public:
     ResultDelegate(lldb::TargetSP target) : m_target_sp(target) {}
     ConstString GetName() override;
     void DidDematerialize(lldb::ExpressionVariableSP &variable) override;
 
     void RegisterPersistentState(PersistentExpressionState *persistent_state);
     lldb::ExpressionVariableSP &GetVariable();
 
   private:
     PersistentExpressionState *m_persistent_state;
     lldb::ExpressionVariableSP m_variable;
     lldb::TargetSP m_target_sp;
   };
 
   /// The language type of the current expression.
   lldb::LanguageType m_expr_lang = lldb::eLanguageTypeUnknown;
+  /// The include directories that should be used when parsing the expression.
+  std::vector<ConstString> m_include_directories;
 
   /// The absolute character position in the transformed source code where the
   /// user code (as typed by the user) starts. If the variable is empty, then we
   /// were not able to calculate this position.
   llvm::Optional<size_t> m_user_expression_start_pos;
   ResultDelegate m_result_delegate;
 
   /// The object (if any) in which context the expression is evaluated.
   /// See the comment to `UserExpression::Evaluate` for details.
   ValueObject *m_ctx_obj;
+
+  /// True iff this expression explicitly imported C++ modules.
+  bool m_imported_cpp_modules = false;
 };
 
 } // namespace lldb_private
 
 #endif // liblldb_ClangUserExpression_h_

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

 #include "lldb/Expression/ExpressionSourceCode.h"
 #include "lldb/Expression/IRExecutionUnit.h"
 #include "lldb/Expression/IRInterpreter.h"
 #include "lldb/Expression/Materializer.h"
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Symbol/Block.h"
 #include "lldb/Symbol/ClangASTContext.h"
 #include "lldb/Symbol/ClangExternalASTSourceCommon.h"
+#include "lldb/Symbol/CompileUnit.h"
 #include "lldb/Symbol/Function.h"
 #include "lldb/Symbol/ObjectFile.h"
 #include "lldb/Symbol/SymbolVendor.h"
 #include "lldb/Symbol/Type.h"
 #include "lldb/Symbol/VariableList.h"
 #include "lldb/Target/ExecutionContext.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/StackFrame.h"
if (target->GetEnableAutoImportClangModules()) {
           }
         }
       }
     }
   }
 }
 
 void ClangUserExpression::UpdateLanguageForExpr(
-    DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx) {
+    DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx,
+    std::vector<std::string> modules_to_import) {
   m_expr_lang = lldb::LanguageType::eLanguageTypeUnknown;
 
   std::string prefix = m_expr_prefix;
 
   if (m_options.GetExecutionPolicy() == eExecutionPolicyTopLevel) {
     m_transformed_text = m_expr_text;
   } else {
     std::unique_ptr<ClangExpressionSourceCode> source_code(
         ClangExpressionSourceCode::CreateWrapped(prefix.c_str(),
                                             m_expr_text.c_str()));
 
     if (m_in_cplusplus_method)
       m_expr_lang = lldb::eLanguageTypeC_plus_plus;
     else if (m_in_objectivec_method)
       m_expr_lang = lldb::eLanguageTypeObjC;
     else
       m_expr_lang = lldb::eLanguageTypeC;
 
     if (!source_code->GetText(m_transformed_text, m_expr_lang,
-                              m_in_static_method, exe_ctx,
-                              !m_ctx_obj)) {
+                              m_in_static_method, exe_ctx, !m_ctx_obj,
+                              modules_to_import)) {
       diagnostic_manager.PutString(eDiagnosticSeverityError,
                                    "couldn't construct expression body");
       return;
     }
 
     // Find and store the start position of the original code inside the
     // transformed code. We need this later for the code completion.
     std::size_t original_start;
     std::size_t original_end;
     bool found_bounds = source_code->GetOriginalBodyBounds(
         m_transformed_text, m_expr_lang, original_start, original_end);
     if (found_bounds) {
       m_user_expression_start_pos = original_start;
     }
   }
 }
 
+static bool SupportsCxxModuleImport(lldb::LanguageType language) {
+  switch (language) {
+  case lldb::eLanguageTypeC_plus_plus:
+  case lldb::eLanguageTypeC_plus_plus_03:
+  case lldb::eLanguageTypeC_plus_plus_11:
+  case lldb::eLanguageTypeC_plus_plus_14:
+  case lldb::eLanguageTypeObjC_plus_plus:
+    return true;
+  default:
+    return false;
+  }
+}
+
+std::vector<std::string>
+ClangUserExpression::GetModulesToImport(ExecutionContext &exe_ctx) {
+  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+
+  if (!SupportsCxxModuleImport(Language()))
+    return {};
+
+  Target *target = exe_ctx.GetTargetPtr();
+  if (!target || !target->GetEnableImportStdModule())
+    return {};
+
+  StackFrame *frame = exe_ctx.GetFramePtr();
+  if (!frame)
+    return {};
+
+  Block *block = frame->GetFrameBlock();
+  if (!block)
+    return {};
+
+  SymbolContext sc;
+  block->CalculateSymbolContext(&sc);
+  if (!sc.comp_unit)
+    return {};
+
+  if (log) {
+    for (const SourceModule &m : sc.comp_unit->GetImportedModules()) {
+      LLDB_LOG(log, "Found module in compile unit: {0:$[.]} - include dir: {1}",
+                  llvm::make_range(m.path.begin(), m.path.end()), m.search_path);
+    }
+  }
+
+  for (const SourceModule &m : sc.comp_unit->GetImportedModules())
+    m_include_directories.push_back(m.search_path);
+
+  // Check if we imported 'std' or any of its submodules.
+  // We currently don't support importing any other modules in the expression
+  // parser.
+  for (const SourceModule &m : sc.comp_unit->GetImportedModules())
+    if (!m.path.empty() && m.path.front() == ConstString("std"))
+      return {"std"};
+
+  return {};
+}
+
 bool ClangUserExpression::PrepareForParsing(
     DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx) {
+  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+
   InstallContext(exe_ctx);
 
   if (!SetupPersistentState(diagnostic_manager, exe_ctx))
     return false;
 
   Status err;
   ScanContext(exe_ctx, err);
 
   if (!err.Success()) {
     diagnostic_manager.PutString(eDiagnosticSeverityWarning, err.AsCString());
   }
 
   ////////////////////////////////////
   // Generate the expression
   //
 
   ApplyObjcCastHack(m_expr_text);
 
   SetupDeclVendor(exe_ctx, m_target);
 
-  UpdateLanguageForExpr(diagnostic_manager, exe_ctx);
+  std::vector<std::string> used_modules = GetModulesToImport(exe_ctx);
+  m_imported_cpp_modules = !used_modules.empty();
+
+  LLDB_LOG(log, "List of imported modules in expression: {0}",
+           llvm::make_range(used_modules.begin(), used_modules.end()));
+
+  UpdateLanguageForExpr(diagnostic_manager, exe_ctx, used_modules);
   return true;
 }
 
 bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
                                 ExecutionContext &exe_ctx,
                                 lldb_private::ExecutionPolicy execution_policy,
                                 bool keep_result_in_memory,
                                 bool generate_debug_info) {
   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
 
   if (!PrepareForParsing(diagnostic_manager, exe_ctx))
bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
 
   if (!exe_scope)
     exe_scope = exe_ctx.GetTargetPtr();
 
   // We use a shared pointer here so we can use the original parser - if it
   // succeeds or the rewrite parser we might make if it fails.  But the
   // parser_sp will never be empty.
 
-  ClangExpressionParser parser(exe_scope, *this, generate_debug_info);
+  ClangExpressionParser parser(exe_scope, *this, generate_debug_info,
+                               m_include_directories);
 
   unsigned num_errors = parser.Parse(diagnostic_manager);
 
   // Check here for FixItHints.  If there are any try to apply the fixits and
   // set the fixed text in m_fixed_text before returning an error.
   if (num_errors) {
     if (diagnostic_manager.HasFixIts()) {
       if (parser.RewriteExpression(diagnostic_manager)) {

lldb/source/Plugins/Platform/Linux/PlatformLinux.h

public:
   void GetStatus(Stream &strm) override;
 
   bool GetSupportedArchitectureAtIndex(uint32_t idx, ArchSpec &arch) override;
 
   int32_t GetResumeCountForLaunchInfo(ProcessLaunchInfo &launch_info) override;
 
   bool CanDebugProcess() override;
 
+  std::vector<std::string>
+  GetSystemIncludeDirectories(lldb::LanguageType lang) override;
+
   lldb::ProcessSP DebugProcess(ProcessLaunchInfo &launch_info,
                                Debugger &debugger, Target *target,
                                Status &error) override;
 
   void CalculateTrapHandlerSymbolNames() override;
 
   MmapArgList GetMmapArgumentList(const ArchSpec &arch, lldb::addr_t addr,
                                   lldb::addr_t length, unsigned prot,

lldb/source/Plugins/Platform/Linux/PlatformLinux.cpp

bool PlatformLinux::CanDebugProcess() {
   if (IsHost()) {
     return true;
   } else {
     // If we're connected, we can debug.
     return IsConnected();
   }
 }
 
+std::vector<std::string>
+PlatformLinux::GetSystemIncludeDirectories(lldb::LanguageType lang) {
+  std::string sys_root = GetSDKRootDirectory().AsCString("");
+  switch (lang) {
+  case lldb::eLanguageTypeC:
+  case lldb::eLanguageTypeC89:
+  case lldb::eLanguageTypeC99:
+  case lldb::eLanguageTypeC11:
+  case lldb::eLanguageTypeC_plus_plus:
+  case lldb::eLanguageTypeC_plus_plus_03:
+  case lldb::eLanguageTypeC_plus_plus_11:
+  case lldb::eLanguageTypeC_plus_plus_14:
+  case lldb::eLanguageTypeObjC_plus_plus:
+    return {sys_root + "/usr/include/"};
+  default:
+    return {};
+  }
+}
+
 // For local debugging, Linux will override the debug logic to use llgs-launch
 // rather than lldb-launch, llgs-attach.  This differs from current lldb-
 // launch, debugserver-attach approach on MacOSX.
 lldb::ProcessSP
 PlatformLinux::DebugProcess(ProcessLaunchInfo &launch_info, Debugger &debugger,
                             Target *target, // Can be NULL, if NULL create a new
                                             // target, else use existing one
                             Status &error) {

lldb/source/Target/Target.cpp

static constexpr PropertyDefinition g_properties[] = {
      "List of directories to be searched when locating debug symbol files. "
      "See also symbols.enable-external-lookup."},
     {"clang-module-search-paths", OptionValue::eTypeFileSpecList, false, 0,
      nullptr, {},
      "List of directories to be searched when locating modules for Clang."},
     {"auto-import-clang-modules", OptionValue::eTypeBoolean, false, true,
      nullptr, {},
      "Automatically load Clang modules referred to by the program."},
+    {"import-std-module", OptionValue::eTypeBoolean, false, false,
+     nullptr, {},
+     "Import the C++ std module to improve debugging STL containers."},
     {"auto-apply-fixits", OptionValue::eTypeBoolean, false, true, nullptr,
      {}, "Automatically apply fix-it hints to expressions."},
     {"notify-about-fixits", OptionValue::eTypeBoolean, false, true, nullptr,
      {}, "Print the fixed expression text."},
     {"save-jit-objects", OptionValue::eTypeBoolean, false, false, nullptr,
      {}, "Save intermediate object files generated by the LLVM JIT"},
     {"max-children-count", OptionValue::eTypeSInt64, false, 256, nullptr,
      {}, "Maximum number of children to expand in any level of depth."},
enum {
   ePropertyPreferDynamic,
   ePropertyEnableSynthetic,
   ePropertySkipPrologue,
   ePropertySourceMap,
   ePropertyExecutableSearchPaths,
   ePropertyDebugFileSearchPaths,
   ePropertyClangModuleSearchPaths,
   ePropertyAutoImportClangModules,
+  ePropertyImportStdModule,
   ePropertyAutoApplyFixIts,
   ePropertyNotifyAboutFixIts,
   ePropertySaveObjects,
   ePropertyMaxChildrenCount,
   ePropertyMaxSummaryLength,
   ePropertyMaxMemReadSize,
   ePropertyBreakpointUseAvoidList,
   ePropertyArg0,

 }
 
 bool TargetProperties::GetEnableAutoImportClangModules() const {
   const uint32_t idx = ePropertyAutoImportClangModules;
   return m_collection_sp->GetPropertyAtIndexAsBoolean(
       nullptr, idx, g_properties[idx].default_uint_value != 0);
 }
 
+bool TargetProperties::GetEnableImportStdModule() const {
+  const uint32_t idx = ePropertyImportStdModule;
+  return m_collection_sp->GetPropertyAtIndexAsBoolean(
+      nullptr, idx, g_properties[idx].default_uint_value != 0);
+}
+
 bool TargetProperties::GetEnableAutoApplyFixIts() const {
   const uint32_t idx = ePropertyAutoApplyFixIts;
   return m_collection_sp->GetPropertyAtIndexAsBoolean(
       nullptr, idx, g_properties[idx].default_uint_value != 0);
 }
 
 bool TargetProperties::GetEnableNotifyAboutFixIts() const {
   const uint32_t idx = ePropertyNotifyAboutFixIts;